Obscuration delineation circuitry

ABSTRACT

A device for providing an indication, on a radial plot, of all the terrain obscured from the view of an assumed observer who is located at some reference elevation above the origin of the plot. The output is obtained by means of an X-Y plotter or coordinatograph. The stylus of the coordinatograph traces a series of radial straight lines from the point corresponding to the observation point. The stylus is lowered to provide a visible record if the terrain is visible from the observation point, and is raised to record a gap if the terrain is obscured or not visible. The device functions by storing a quantity representative of the largest value of the look angle, as the terrain is scanned from the center outward, and treats all terrain with a look angle smaller than any previous look angle as obscured.

sew-e20 W United States Patent 51 3,671,729

Lux 1 June 20, 1972 s41 OBSCURATION DELINEATION 3,517,122 6/1970 Owen..35/10.2 x CIRCUHTRY 3,539,696 1 1/1970 Sweeney et al. ..35/ 10.2

[72] lnventor: Foss Britton Lux, Oak Park, Mich. 48237 primary Emmine,-Jseph Ruggiero 73 Assignee: The United States of America as representedAttorney-Harry Herbert and George Fine by the Secretary of the Air Force[57] ABSTRACT [22] filed: March 1971 A device for providing anindication, on a radial plot, of all the [21] Appl. No.: 122,707 terrainobscured from the view of an assumed observer who is located at somereference elevation above the origin of the plot. The output is obtainedby means of an X-Y plotter or [52] U.S.Cl. ..235/ 186, 35/102,coordinatograph. The stylus of the coordinatograph traces a [51] Int ClG06 7/22 series of radial straight lines from the point corresponding to[58] i 4 the observation point. The stylus is lowered to provide a visiuble record if the terrain is visible from the observation point, and israised to record a gap if the terrain is obscured or not 56] ReferencesCited visible. The device functions by storing a quantity representativeof the largest value of the look angle, as the terrain is UNITED STATESPATENTS scanned from the center outward, and treats all terrain with a3,060,596 10/1962 Tucker et al ..35 10.2 angle Smaller than any previouslook angle as obscured I 3,439, 1 Ct 3| 3 5 Drawing Figures BACKGROUNDOF THE INVENTION The present invention relates broadly to an. automatedchart analysisapparatusand in particular to anobscurationtdelineationapparatusprovidi gan indication of all theterrain which is obscured fromview of some reference elevation on a radial plot.

In the prior art, it was, possible to determine points in view from agivenobservation. and along a particular line of sight by noting theintersected elevation interval lines. This process was generallyconducted manually and was extremly slow and tedious. There was alwaysthe ever present danger offalse information due to human error ormistake. As an alternative method of determining points along a givenline of sight, it is also feasible to. describe the various pointsinvolved by means of rectangular coordinates. However, it has been,found that merely knowing the location of any given point in rectangularcoordinates or the horizontal and vertical distance from: theobservation point, provides very little information as to whether thatparticular point is visible from, the observation point. Various pointsmay. be visible whether they 'areabove or below the observation pointand various. other points which also may be above or below theobservation point may-be obscured. Further, knowing the polarcoordinates of a point on the line of sight profile will not provide anydata to allow determination of whether the point is obscured or not,unless the coordinates of all points-closer to the observation point arealso known. The present invention will automatically provide an terrainprofile plot along a given line andwill provide-an indication forallpoints whichl may be viewedfrom a given observation point and alsoforthose points which are obscured from view.

SUMMARY The present. invention utilizes an AC resolver to continuouslycompare a vertical distance, AE, to a horizontal 2 DESCRIPTION OFPREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a blockdiagram of the obscuration delineation circuit utilizing-a resolver toreceive input signals, AE, Y7, where AE is the vertical distance and- Y7is the horizontal distance. The output signals from resolver 10 areconnected to AGC unit 11. The obscuration detection circuit receives anoutput signal, sin Aa, from the AGC unit I 1 and provides a controlsignal to the servo amplifier and motor 13 and a stylus control signal.Theservo amplifier and motor unit 13 is mechanical linked to resolver10. The obscuration delineation circuit provides a visual indication, ona radial plot, of all the terrain obscured from the view of an assumedobserver who is located at some reference elevation above the origin ofthe radial plot. The output is obtained by means of an XY plotter, orcoordinatograph (neither apparatus shown). The stylus (not shown of thecoordinatographtraces a series of radial straightlines from the pointcorrespondingto the observation point. 'I'hestylus is lowered to providea visible record if the terrain is visible from the observation point,and is raised to record a gap if the terrain is obscured or not visible.An AC resolver 10 is used to continuto. perform the same basicoperations. It is not necessary to form the arctangent (angle whosetangent is the ratio) AE/ Y'y, as the ratio could be used directly todetermine whether the terrain is obscured. However, the arctangentmethod allows distance, {7, to provide an angle whose tangent is equalto the ratio AE/ Y-y. This obscuration data provides an indication on aradial plot of allthe terrainwhich is obscured from the view ofanobserver who is located-at an referenceelevation abovethe origin ofthe radial plot. The stylus ofa coordinatographtraces a series of radialstraight lines from the point which corresponds to the observationpoint. The stylus is lowered to provide-a visible record if the terrainisvisible from the observation point and is raised to record a gap ifthe terrain is obscured or not visible.

It is one object of the invention, therefore, toproyide an obscurationdelineation circuit having a visual indication on aradial plot of allterrain which is obscured from view.

It is another object of the invention to provide an obscurav' tiondelineation circuit having the capability of determining whether pointswhich are above or below the observation point are obscured from view.

It is yet another object of the invention to provide an obscurationdelineation circuit having the capability of detecting whether an objecthaving a given height above the ground is obscured.

DESCRIPTION OF DRAWINGS the present invention, and

FIG. 5 is a block diagram of the obscuration delineation cir-v cuit withthe obscured terrain modification included.

either of the inputs to go through zerowithout causing the difficultiesusually associated with division by terms at or near zero. I

Each point on the profile can be located within the plane by specifyingits horizontal distance from the point of observation, 0, and itsvertical distance from the point 0. This corresponds. to using arectangular coordinate system. Each point can also be located byspecifying its distance, D, from O and the angle of elevation, at. Theangle of elevation as herein used is the angle between a vertical line,through the-observation point, and a straight line passing through theobservation point and the point whose location is being specified. Thiscorresponds to using a polar coordinate system.

A point will be obscured only .if its angle ofelevation is smaller thanthe angle of some other point whose distance from the observation pointis less than that of the present point. It may be seen that elevationangle of each succeeding point from the observation reference point mustbe equal to or larger than the previously determined angles in order tobe visible. As the points on a profile or contour map are examined fromthe observation point, 0, outward, the present point-under considerationwill have a larger distance, D, than all other previous points (i.e.,these previous points are closer to the observation point, 0). As thepoints on a profile or contour map are examined from the observationpoint 0 outward so that at any point, all previous points have a smallerD (are closer to 0) than the present point. Therefore, to be obscured itissuficient that some previous point have had an elevation angle largerthan the present point. Thus, it is only necessary to store the largestvalue of a for all past points and to treat as obscured all new pointswhich have a smaller elevation angle than the storedvalue. The value ofa is obtained by means of an arctangent servo.

The storing of the maximum angle is accomplished by the obscurationdelineation circuit by inhibiting the arctangent servo, which is used tocompute elevationangle, whenever the error signal has a polarity suchthat the output angle would normally become smaller. FIG. 3 is aschematic diagram of the obscuration detection circuit which providescontrol signals to the servo amplifier and motor, 13 in FIG. 1 and thestylus control signal. A first circuit having an input terminal 20, anoperational amplifier 21, an N-P-N transistor 22, and an output terminal23, is used to detect where the error signal is of this polarity, whichis defined as a negative signal and to provide a control signal to theservo amplifier and motor unit 13. The level at which the inhibitingaction takes place is adjusted to be a more positive (less negative)level than that required to move the servo in a negative direction. Asecond circuit utilizing transistors 24, 25, 26 input terminal 20, andoutput terminal 27 provide a stylus control signal. The second circuitis adjusted by means of relay control 28 so that it detects a slightlymore negative error signal than that required for the inhibiting action,and produces a signal which causes the terrain to be plotted asobscured. A relay contact (not shown), which is activated by the samecircuits that cause the plotter to start over at the origin, is used tobypass the inhibit circuit and allow the arctangent servo to reset to azero angle.

In chart analysis devices which may be utilized to provide the inputsignals to the present invention, the profile information is generallyavailable in rectangular coordinate form. The

elevation measurement from the plotter is subtracted from the referenceelevation to produce the vertical coordinate AE. The horizontal distancefrom the origin, Y'y, is available from the plotting motion controller.The relationship between the rectangular coordinates AE, Y7 and thepolar coordinates D, a can be expressed as Y =Dsina and AE=Dcosa (2) orD=(Yy +AE a and a arctangent Y'y/AE 4 An AC resolver 30 is utilized aspart of an arctangent servo to convert the profile information into itspolar form. FIG. 2 is a block diagram of a resolver. The AC resolver 30is particularly convenient to use because the available inputs are inthe form of AC voltages. The AC resolver 30 is a device that has twoorthogonal input windings and two orthogonal output windings arranged sothat the amount of coupling between the input windings and the outputwindings can be controlled by a mechanical shaft input 31. Theconstruction is such that if AE and Y-y are assumed to be the twoinputs, the two outputs will be E,==AE cos a+ Yy sin a (5) and E Y'y cosa AEsin a (6) E, D cos A0: (9) and E =Dsin Act (10) where Aa=a-a If a ismade equal to a, the quantity E becomes zero, and for small differencesbetween a and a, the quantity E may be used to indicate the magnitude ofthe difference, or error. When the resolver is used as part of anarctangent servo, E is used as the activating signal to drive the servoto null. Normally the servowill continue to run until E is essentiallyzero and the resolver shaft angle a is equal to a, as defined inequation As discussed previously, the arctangent servo is allowed,tooperate normally as long as the angle a is increasing orrernainingconstant. However, the obscuration detection circuit prevents a negativeerror from causing the angle a to become smaller. The negative error isdetected and used to inhibit the servo and to indicate an obscured area.The inhibit portion of the circuit may be bypassed whenever the plotteris reset.

The obscuration circuit determines what terrain is obscured from viewfrom a central point but does not indicate to what extent the terrain isobscured. For instance, it does not provide any data or information thatan object at a given height, h, above the terrain would be obscured fromthe observation point. The ability to detect whether an object at heighth above the ground is obscured, is a desirable feature. In order todetermine this, itis necessary to develop a signal, V, proportional tothe vertical distance from each point on the terrain profile, to theline of sight, and compare this signal with a second signal representingthe quantity, h. If V is found to be greater than h then the point isconsidered to be obscured and the stylus would be lifted. FIG. 4 shows asection of a terrain profile having points 1-4 at different distancesand elevations with respect to the observation point, 0. In the presentobscuration circuit, the obscured terrain would be indicated for theterrain between points 3 and 4. However, the terrain does not drop belowthe line of sight by a distance equal to h until point 4 is reached.Therefore, an object having a distance h above the terrain point beingplotted, would not become obscured from the observation point until theplot passes through point 4 and the stylus should be lifted at point 4.However, the arctangent servo is required to continuously store thelargest elevation angle encountered along the profile. Therefore itwould have been inhibited at point 3. As shown by equation (10) the Eoutput of the resolver at point 4 will be E D sin Act. This is a signalwhich represents the shortest distance from the line of sight to theterrain point 4 or the distance from the line of sight down to the pointon the terrain profile measured at right angles to the line of sight.This distance would be shorter than the vertical distance by the factorsin a as shown in FIG. 2. Thus, for a line of sight within 1 11 ofhorizontal (a' the error would be less than 2 percent. The error wouldreach 5 percent at angles greater than 18, and 10 percent at anglesgreater than 1 25. When compared to the possible error in measuring theactual elevation, this may be permissable.

Referring now to FIG. 5, the modification of the circuit shown in FIG. Iwould be as follows: a potentiometer 50 would be added which would beused to introduce the height, h, of an object above the ground. Thequantity h would be summed with the signal D sin A0: in the preampdemodulator unit 52 to provide a signal which indicates an obscuredarea. An additional detector circuit 54 would be required because thepresent circuit is combined with the circuit which determines when theservo is to be inhibited and cannot be separated. Therefore, theexisting pen lift circuit of the obscuration detection circuit isduplicated to provide the new pen lift signal. If the error which isintroduced by the fact that D sin Aa is not measured vertically is notacceptable, a correction factor can be introduced by adding an extraresolver to the arctangent servo. Then by dividing the quantity D sinAct by sin a the true vertical measurement can be obtained. However, itis preferable to convert the height input by multiplying h by sin a toproduce a scaled h to match D sin A0: as shown in FIG. 5.

While in accordance with the provisions of the statutes, we haveillustrated and described the best forms of the invention now known tous, it will be apparent to those skilled in the art that changes may bemade in the form of the apparatus disclosed without departing from thespirit of the invention as set forth in the appended claims, and that insome cases certain features of the invention may be used to advantagewithout a corresponding use of other features.

I claim:

1. An obscuration delineation circuit providing control signals to anautomated chart analysis apparatus comprising in combination:

an AC resolver having a first and second input winding, a put windings.

first and second output winding and a mechanical input 2. An obscurationdelineation circuit as described in claim 1 shaft, said first and secondinput winding being coupled to wherein said obscuration detectioncircuit comprises: said first and second output winding, said mechanicala first circuit to detect the polarity of said signal from said inputshaft controlling the amount of coupling between 5 AGC unit, said firstcircuit providing a control signal to said first and second inputwinding and said first and inhibit motion of said servo unit in anegative direction second output winding, said f'u'st and second inputwindn Said C Signal is negative, ing receiving an input signal from saidchart analysis apa second circuit to detect an error signal from saidAGC paratus, said first and second output winding providing Unit moregati n required for aid inhibiting output signals, 10 signal, saidsecond circuit providing said terrain obscuraan AGC unit connected tosaid first and second output tion Signalwinding to receive said outputsignals, said AGC uni 3.An0bscuration delineation circuitasdescribed inclaim 1 providing an output signal, further including an obscurationdetection circuit to detect the polarity of a potentiometer having areference Voltage pp said said output signal from said AGC unit, saidobscuration l5 potentiometer being adjusted to Provide an Outputvoltdetection circuit providing an inhibit signal when said age whichrepresents the heishwfan j output signal from said AGC unit is negative,said inhibit an amplifier demOdulatol' to Sum Said output Whale withsaid output signal from said resolver, said summed signal being theoutput of said amplifier demodulator, and an obscuration detectioncircuit connected to said amplifier demodulator unit to receive said sumsignal, said obscuration detection circuit providing an output pen lifisignal, a resolver driven by said arctangent servo which providescorrections to the height comparison circuit when the look angle is nothorizontal.

i t III II signal being utilized by said chart analysis apparatus toindicate as obscure, the terrain being plotted, said inhibit signalbeing the stylus control signal to said chart analysis 20 apparatus,said obscuration detection circuit providing a servo control signal,and,

a servo amplifier and motor unit receiving said servo control signal,said servo unit being connected to said mechanical input shaft of saidresolver, said servo unit controlling the amount of coupling betweensaid resolver input and out-

1. An obscuration delineation circuit providing control signals to anautomated chart analysis apparatus comprising in combination: an ACresolver having a first and second input winding, a first and secondoutput winding and a mechanical input shaft, said first and second inputwinding being coupled to said first and second output winding, saidmechanical input shaft controlling the amount of coupling between saidfirst and second input winding and said first and second output winding,said first and second input winding receiving an input signal from saidchart analysis apparatus, said first and second output winding providingoutput signals, an AGC unit connected to said first and second outputwinding to receive said output signals, said AGC unit providing anoutput signal, an obscuration detection circuit to detect the polarityof said output signal from said AGC unit, said obscuration detectioncircuit providing an inhibit signal when said output signal from saidAGC unit is negative, said inhibit signal being utilized by said chartanalysis apparatus to indicate as obscure, the terrain being plotted,said inhibit signal being the stylus control signal to said chartanalysis apparatus, said obscuration detection circuit providing a servocontrol signal, and, a servo amplifier and motor unit receiving saidservo control signal, said servo unit being connected to said mechanicalinput shaft of said resolver, said servo unit controlling the amount ofcoupling between said resolver input and output windings.
 2. Anobscuration delineation circuit as described in claim 1 wherein saidobscuration detection circuit comprises: a first circuit to detect thepolarity of said signal from said AGC uNit, said first circuit providinga control signal to inhibit motion of said servo unit in a negativedirection when said AGC signal is negative, and, a second circuit todetect an error signal from said AGC unit more negative than requiredfor said inhibiting signal, said second circuit providing said terrainobscuration signal.
 3. An obscuration delineation circuit as describedin claim 1 further including a potentiometer having a reference voltageapplied, said potentiometer being adjusted to provide an output voltagewhich represents the height of an object, an amplifier demodulator unitto sum said output voltage with said output signal from said resolver,said summed signal being the output of said amplifier demodulator, andan obscuration detection circuit connected to said amplifier demodulatorunit to receive said sum signal, said obscuration detection circuitproviding an output pen lift signal, a resolver driven by saidarctangent servo which provides corrections to the height comparisoncircuit when the look angle is not horizontal.